Air-conditioning apparatuses include an air-conditioning apparatus configured like, for example, a multi-air-conditioning apparatus for a building, such that a heat source unit (outdoor unit) is disposed outside a structure and an indoor unit is disposed in an indoor space in the structure. Refrigerant circulated through a refrigerant circuit included in the air-conditioning apparatus transfers heat to (or removes heat from) air supplied to a heat exchanger in the indoor unit, thus heating or cooling the air. The heated or cooled air is sent to an air-conditioned space, thus performing heating or cooling.
A typical building has a plurality of indoor spaces and such an air-conditioning apparatus accordingly includes a plurality of indoor units. In a large building, refrigerant pipes connecting the outdoor unit to each indoor unit may have a length of 100 m. The longer the pipes connecting the outdoor unit to each indoor unit are, the more the amount of refrigerant with which the refrigerant circuit is filled is needed.
Indoor units of a multi-air-conditioning apparatus for a building are typically installed and used in indoor spaces (e.g., an office space, a living room, and a store) where people stay. Some of refrigerants are flammable and toxic to humans. If such a refrigerant leaks out of any indoor unit disposed in an indoor space for some reasons, the refrigerant may significantly affect human health and cause safety issues. If a refrigerant which is harmless to humans leaks out of any indoor unit, the concentration of oxygen in the indoor space may decrease due to the refrigerant leakage and accordingly affect human health. A method using an air-conditioning apparatus of a two-loop system type including a primary loop through which refrigerant is circulated and a secondary loop through which water or brine that is harmless is circulated for air conditioning in a space where people stay has been proposed to overcome the above-described disadvantages (refer to Patent Literature 1, for example).
In particular, in Patent Literature 1, three-way valves and flow control valves in a heat medium circuit are controlled by a valve control circuit including a microcontroller. The valve control circuit cannot drive a plurality of valve mechanisms at the same time. This circuit transmits drive signals to the valve mechanisms at different times.